Prime Minister Shinzo Abe has decided to visit Moscow in May to attend a ceremony marking the 75th anniversary of Russia’s victory over Germany in World War II and to hold talks with President Vladimir Putin, a Japanese government source said Friday.

Japan and Russia are trying to arrange a meeting between Abe and Putin on May 8 or May 10, according to the source. The ceremony will be held on May 9.

“He is invited to the ceremony. There is no reason to turn it down,” the source said.

Abe is expected to meet Putin to strengthen their personal relationship and promote territorial talks over the four disputed Russian-held islands off Hokkaido.

In the meantime, Abe pledged on Friday to advance bilateral talks on signing a peace treaty with Russia as supporters of Russia returning the four islands to Japan held an annual rally in Tokyo.

For the second year in a row, participants in the event refrained from calling the Russian occupation of the islands “illegal,” apparently to avoid raising bilateral tensions over the territorial issue.

“I will step up joint work to find a solution that is acceptable to both sides and advance (peace treaty) negotiations steadily,” Abe said at the rally, which is usually held on Feb. 7.

Abe has been seeking to resolve the decades-old territorial dispute and conclude negotiations for a postwar peace treaty. But the two nations have made little headway due to a huge gap over the status of the islands.

Russia wants Japan to recognize that the islands were legitimately acquired following Tokyo’s 1945 surrender in World War II. Japan, however, has taken the view that the seizure was illegal.

Participants including public and private groups adopted a statement calling for the return of what they described as Japan’s “inherent” territories at an early date.

Still, they apparently took heed of the ongoing peace treaty talks and did not say the islands are illegally occupied — wording that could irritate Russia.

In the previous rally last year, the phrase “illegal occupation” was dropped.

Abe told the crowd at the annual event that bilateral talks on joint economic projects on the disputed isles have progressed, adding that he hopes to pursue them “without undermining the legal positions of Japan and Russia” regarding the territories.

The joint economic projects are designed to build mutual trust and pave the way for resolving the territorial issue that has prevented Tokyo and Moscow from signing a postwar peace treaty.

Abe and Putin agreed in 2018 to step up peace treaty negotiations based on a 1956 joint declaration between Japan and the former Soviet Union. The document states that two of the four islands — Shikotan and the Habomai islet group — will be handed over to Japan following the conclusion of a peace treaty.

Abe has put his weight behind achieving the return of two islands rather than all four. The other two are Etorofu and Kunashiri.

Russia is concerned about the prospect of a U.S. military presence forming should any of the islands return to Japan, as Tokyo and Washington are longtime security allies.

On Feb. 7, 1855, Japan and Russia concluded the Treaty of Commerce, Navigation and Delimitation, drawing a national border that put the four islands in Japanese territory.